Conventionally, as a method of diagnosing leakage in piping of evaporated fuel, there has been established a method of pressurizing the piping by an air pump after sealing the piping, and diagnosing a leakage amount in the piping based on a pressure variation in the piping or a load to the air pump at that time. Then, as the air pump to be used for the diagnosis, a vane pump as one of positive displacement pumps is popular.
Major components of the vane pump are a cylindrical rotor, thin plate vanes, and a cylindrical housing that houses them. The rotor is installed at a position eccentric from the center of the housing, and the vanes are installed slidably in slits provided on outer peripheral portions of the rotor. With rotation of the rotor, the vanes slide in a radial direction inside the slits, so that the vanes rotate while maintaining a close contact state between an inner wall surface of the housing and end portions of the vanes. When the vanes rotate with keeping the close contact with the housing wall surface, there is generated a sealed space which is surrounded by the rotor, the housing, and the vanes; a volume of the space changes continuously with the rotation of the rotor, and thus a function as the air pump is established. A gas is sent out in such a manner that the space is connected to an intake port at a volume expanding timing, and connected to a discharge port at a volume reducing timing.
The rotor of the vane pump is rotationally driven by a motor, and the rotor and the motor are connected to each other such that a motor shaft is inserted into a hole bored in a center part of the rotor. In order to absorb axial deflection of the motor shaft, a variation in component dimensions, and a dimensional variation thereof due to temperature changes, etc., a certain clearance is necessary between the motor shaft and the rotor hole; however, due to the provision of the clearance, the rotor cannot be completely fixed, which causes a rotor vibration. In particular, under a high-load condition, there is a matter such that the rotor vibrates extremely to generate abnormal sound and also reduce a flow characteristic thereof.
In addition, because a characteristic of the air pump strongly influences accuracy of the air pump-based diagnosis for the leakage in the piping, highly accurate dimensions are required for the vane pump to be used as the air pump. As a result, there are problems such that cost of the components increases, and that the diagnostic accuracy reduces because of a variation in the characteristic due to abrasion associated with usage.
Accordingly, in Patent Documents 1 and 2, for example, it is adapted that since a rotor is inclined to an axial direction of a motor shaft, during rotation of a motor, vibrations of the rotor are suppressed by setting the rotor in a state that an outer edge part of the rotor is in sliding contact with a housing. Further, according to Patent Document 3, for example, it is adapted that since slits that house vanes are inclined to an axial direction of a motor shaft, during rotation of a motor, vibrations of a rotor are suppressed by setting the rotor in a state that the vanes move in the axial direction by force received from the gas so that the vanes are pressed against a housing wall surface.